lex.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)lex.1	8.2	9/27/90
.TH lex 1
.SH Name
lex \- generate lexical analyzer
.SH Syntax
.B lex
[\fB\-tvfn\fR] \fIfile...\fR 
.SH Description
.NXR "lex program generator"
.NXR "lexical analysis program" "generating"
.NXA "yacc compiler" "lex program generator"
The 
.PN lex
command
generates programs to be used in simple lexical analysis of text.
The input
.I files
(standard input default) contain regular expressions
to be searched for, and actions written in C to be executed when
expressions are found.
.PP
A C source program, 'lex.yy.c', is generated.  It is compiled 
using the following command line:
.EX
cc lex.yy.c \-ll
.EE
This program copies unrecognized portions of
the input to the output, and executes the associated
C action for each regular expression that is recognized.
.SH Options
.NXR "lex program generator" "options"
.IP \fB\-f\fR 5
Runs a faster compilation (does not pack resulting tables).
This is limited to small programs.
.IP \fB\-n\fR 
Prints no summary information (default option).
.IP \fB\-t\fR 
Writes to standard output instead of to file 
.PN lex.yy.c .
.IP \fB\-v\fR 
Prints one-line summary of generated statistics.
.SH Examples
.NXR "lexical analysis program" "example"
In the following example, the command
.EX
lex lexcommands
.EE
draws
.PN lex
instructions from the file
.IR lexcommands ,
and places the output in lex.yy.c.
The command
.EX
%%
[A\-Z]	putchar(yytext[0]+\'a\'\-\'A\');
[ ]+$
[ ]+	putchar(\' \');
.EE
.PP
is an example of a
.PN lex
program that would be put into a
.PN lex
command file.  This program converts upper case to lower,
removes blanks at the end of lines,
and replaces multiple blanks by single blanks.
.SH See Also
sed(1), yacc(1)
.br
"LEX \- Lexical Analyzer Generator",
\fISupplementary Documents, Volume 2: Programmer\fP